Echinoderms

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Echinoderms

• Developed By Adam F Sprague Dave Werner
• MATES Biology
• (Marine Bio Book Ch.7)
• (Biology Book Ch.40)

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5 classes of Echinoderms

• Sea star or starfish (Asteroidea)
• Brittle stars, basket stars, serpent stars
  (Ophiuroidea)
• Sea urchins, heart urchins and sanddollars
  (Echinoidea)
• Holothurians or sea cucumbers (Holothuroidea)
• Feather stars and sea lilies (Crinoidea).

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Characteristics of Echinoderms

• radial symmetry
• body 5 equal segments, each containing
  duplicate set of internal organs
• Pentamerous radial symmetry
• no heart, brain, eyes, but some brittle stars
  have light sensitive parts on arms
• Mouth-situated on underside anus on top (except
  feather stars, sea cucumbers some urchins).

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Characteristics of Echinoderms

• tentacle-like structures tube feet w/ suction
  pads
• tube feet -hydraulically controlled by vascular
  system- supplies water through canals
• Water creates suction effect

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Ecology and range of Echinoderms

• exclusively marine
• occur in various habitats from intertidal zone to
  bottom of deep sea trenches from sand to rubble
  to coral reefs and in cold and tropical seas.

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Behavior of Echinoderms

• Some carnivorous (i.e. sea star), detritus
  foragers (i.e. sea cucumbers) or planktonic
  feeders (i.e. basket stars)
• Reproduction carried out by release of sperm
  eggs into water. Most species produce pelagic (
  free floating) planktonic larvae which feed on
  plankton

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Behavior of Echinoderms

• can regenerate missing limbs, arms, spines - even
  intestines (i.e. sea cucumbers).
• Some brittle stars sea stars can reproduce
  asexually by breaking a ray or arm or by
  deliberately splitting the body in half. Each
  half whole new animal.

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Sea stars (starfish)(Asteroidea) Characteristics

• radial symmetry, several arms (5 or multiplied by
  5) radiating from a central body
• Mouth anus close together
• water intake (madreporite)
• upper surface is often very colorful.
• Minute pincer-like structures called pedicellaria
  are present. These structures ensure that the
  surface of the arms stay free from algae.
• underside is often a lighter color

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Sea stars (starfish)(Asteroidea)

• Ecology and range or sea stars
• The starfish lives everywhere in the coral reef
  and on sand or rocks

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Sea stars (starfish)(Asteroidea)

• Behavior of sea stars
• majority are carnivorous -feed on sponges,
  bryozoans, ascidians molluscs
• detritus feeders (detritus organically enriched
  film that covers rocks) or scavengers.
• Some are specialized feeders, i.e.
  crown-of-thorns feeds on live coral polyps.

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Sea stars (starfish)(Asteroidea)

• Behavior of sea stars
• regeneration
• (asexual reproduction autotomy)
• In others the body is broken into unequal parts
  ( fission) then the missing limbs regenerate

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Anatomy of an adult sea star. Lower (right)
image is a cross section through an arm of the
adult sea star. Images from Purves et al., Life
The Science of Biology, 4th Edition, by Sinauer
Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
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Sea urchin(Echinoidea)

• Characteristics of sea urchins
• Radial symmetrical body with external chitinous
  skeleton and a centrally located jaw (called
  Aristotle's lantern) with horny teeth
• mouth consists of a complex arrangement of
  muscles and plates surrounding circular opening
• The anus is located on the upper surface. Some
  sea urchins have a spherical, bulb like cloaca
  (to store fecal material) that protrudes from the
  anal opening. can be withdrawn into shell.

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Sea urchin(Echinoidea)

• Ecology and range of sea urchins
• Rubble and sand. An abundance of sea urchins can
  be a sign for bad water conditions

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Sea urchin(Echinoidea)

• Behavior of sea urchins
• Locomotion by tube feet spines
• generally nocturnal
• Most are algal grazers -some feed on sponges,
  bryozonans and ascidians and others on detritus
  (detritus organically enriched film that covers
  rocks).
• The sexes are separate young are formed
  indirectly by the fusion of sperm and eggs
  released into the water.

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Sea CucumbersHolothurians (Holothuroidea)

• Characteristics of sea cucumbers
• holothurians are bilateral (distinct dorsal and
  ventral side)
• as name suggests, they are cucumber shaped w/ an
  elongated, muscular, flexible body w/ mouth at
  one end anus at the other. Tentacles around
  mouth (modified tube feet) used in food
  collecting

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Sea CucumbersHolothurians (Holothuroidea)

• Ecology and range of sea cucumbers
• Rubble, rocks and sand. Also seen on some sponges
  in large aggregations.

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Sea CucumbersHolothurians (Holothuroidea)

• Behavior of sea cucumbers
• Most species feed on rich organic film coating
  sandy surfaces
• crawl over bottom ingesting sand. The edible
  particles (organic matter such as plankton,
  foraminifera and bacteria) are extracted when
  passing through their digestive tract processed
  sand is expelled from anus (as worm-like
  excrements).

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Sea CucumbersHolothurians (Holothuroidea)

• Behavior of sea cucumbers
• move by means of tube feet
• When attacked they shed a sticky thread like
  structure which is actually parts of their guts.
  The so called Cuverian threads are toxic (the
  poison is called holothurin) and can dissuade
  many potential predators. These structures
  quickly regenerate.

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Feather stars(Crinoidea)

• Characteristics of feather stars
• Characteristics of feather stars
• AKA- crinoids.
• radial symmetry
• The body is cup-shaped, their numerous feathery
  arms project from a central disc
• 5-200 arms, called pinnules-coated w/sticky
  substance to catch food.
• appendages known as cirri attached to the
  underside of the body with which they cling to to
  sponges or corals.
• mouth and their anus on upper side.

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Feather stars(Crinoidea)

• Ecology and range of feather stars
• primarily nocturnal but seen in the open during
  the day with arms rolled up.
• Crinoid stalks and blastoid heads are common
  fossils in certain parts of North America.
• Specimen of the Carboniferous crinoid
  Paradichocrinus planus

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Feather stars(Crinoidea)

• Behavior of feather stars
• Feather stars can crawl, roll, walk and even swim
  but usually they cling to sponges or corals.
  Feather stars are very abundant in areas exposed
  to periodic strong currents, because they feed on
  planktonic food.

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Brittle stars(Ophiuroidea)

• Characteristics of brittle stars
• Characteristics of brittle stars
• close relatives of sea stars
• radial symmetry-five snakelike arms
• no replication of internal organs, just one set
  in the central disk
• Compared to starfish, brittle stars have a much
  smaller central disc and no anus
• Wastes are eliminated through the mouth on
  underside

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Brittle stars(Ophiuroidea)

• Ecology and range of brittle stars
• very cryptic hide in crevices under corals
• Best seen at night time, when they emerge to
  feed on plankton. Usually at places exposed to
  strong currents.

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Brittle stars(Ophiuroidea)

• Behavior of brittle stars
• Brittle arms an escape mechanism.
• arms regenerate quickly and an entire new
  organism can regenerate, if the broken arm is
  attached to a seizable portion of the disk
• reproduce asexually by self-division
• Brittle stars are the most active and fastest
  moving echinoderms

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Why are the echinoderms the most advanced of the
invertebrates?
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The answer lies in the development of the embryo.
If you were to watch an embryonic starfish
develop, you would see that it begins life
bilaterally, but switches to radial symmetry as
it matures.

• Deuterostome means "mouth second
• In the earliest stages of embryo development,
  when there are only a few cells and the embryo
  resembles a tiny globe of cells, a small pucker
  develops on one side of the embryo. This grows
  into a pocket, and allows some cells to migrate
  inside to form an additional layer of cells
  within the outer layer.
• At this stage, the embryo is known as a gastrula.
  In the Protostomia, which is the other major
  group of the Bilateria, the mouth develops from
  the edge of this pocket, where the inner and
  outer layer of cells meet the anal opening
  develops later.
• In the Deuterostomia, the reverse is true the
  pocket edge develops into the anus, and the mouth
  is formed later. "Your mouth comes second."
• http//www.ucmp.berkeley.edu/phyla/deuterostomia.h
  tml

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http//www.pgjr.alpine.k12.ut.us/science/whitaker/
Animal_Kingdom/SeaStar/SeaStar.html http//www.oc
c.cccd.edu/faculty/mperkins/zoo-review/sea-star/